1. Field of the Invention
The present invention relates to an image forming apparatus which performs printing on both faces of a recording medium, a control method for the image forming apparatus, and a storage medium.
2. Related Background Art
In recent years, an image forming apparatus which transfers yellow, magenta, cyan and black images on a sheet (a recording medium) in an electrophotographic process, fixes formed toner images to the sheet by a fixing roller, and then discharges the sheet to perform two-faced printing is widespread.
As shown in FIG. 6, in case of the two-faced printing by the image forming apparatus, for example, a transportation roller 326 is reversed after the trailing edge of the sheet passed a sheet discharge sensor 324, the sheet is thus switched back, and then the image is again formed on the back face of the sheet through a reverse rotation path 325.
FIG. 7 is a block diagram showing a control structure of the conventional image forming apparatus. Hereinafter, the control structure of the conventional image forming apparatus will be explained.
In FIG. 7, numeral 401 denotes a CPU which controls the image forming apparatus as a whole, and numeral 402 denotes a DC (direct current) brushless motor which drives a photosensitive drum for yellow (called a Y photosensitive drum). The DC brushless motor 402 drives each roller of an yellow (Y) cartridge 314, a Y photosensitive drum 306, and a transfer roller for yellow (called a Y transfer roller) 310 shown in FIG. 6.
Numeral 403 denotes a DC brushless motor which drives a photosensitive drum for magenta (called an M photosensitive drum). The DC brushless motor 403 drives each roller of a magenta (M) cartridge 315, an M photosensitive drum 307, and a transfer roller for magenta (called an M transfer roller) 311 shown in FIG. 6.
Numeral 404 denotes a DC brushless motor which drives a photosensitive drum for cyan (called a C photosensitive drum). The DC brushless motor 404 drives each roller of a cyan (C) cartridge 316, a C photosensitive drum 308, and a transfer roller for cyan (called a C transfer roller) 312 shown in FIG. 6. Numeral 405 denotes a DC brushless motor which drives a photosensitive drum for black (called a Bk photosensitive drum). The DC brushless motor 405 drives each roller of a black (Bk) cartridge 317, a Bk photosensitive drum 309, and a transfer roller for black (called a Bk transfer roller) 313 shown in FIG. 6.
Numeral 406 denotes a high voltage control circuit which applies a high voltage based on the electrophotographic process to the photosensitive drums, the cartridges, the transfer rollers and an electrostatic belt and controls the applied voltage. The high voltage control circuit 406 contains control circuits for four colors. Numeral 407 denotes a scanner control circuit which scans the photosensitive drum with a laser beam. Also, the scanner control circuit 407 contains control circuits for the four colors.
Numeral 408 denotes a fixing control circuit which controls a temperature of a fixing heater, and numeral 409 denotes a sheet discharge sensor. Numeral 410 denotes a DC brushless motor which drives the fixing roller and the electrostatic belt. Namely, the DC brushless motor 410 controls an electrostatic belt 305 and a fixing roller 322 shown in FIG. 6. Numeral 411 denotes a pulse motor which drives a sheet feed roller. Namely, the pulse motor 411 drives a sheet feed roller 303 shown in FIG. 6. Numeral 412 denotes a pulse motor which is used to perform the two-faced printing. Namely, the pulse motor 412 drives the transportation roller 326 shown in FIG. 6.
Numerals 413 and 414 denote driver (D/V) IC""s for the pulse motors. Each of the D/V IC""s 413 and 414 performs constant current control to flow a desired current in a desired excitation phase on the basis of an excitation signal supplied from the CPU.
Numeral 415 denotes an interface which communicates with a not-shown host computer.
As above, the color image forming apparatus includes the plural driving motors, and uses them according to an object. The respective motors are started, controlled and stopped by the control CPU.
FIG. 8 is a block diagram showing a circuit structure of the conventional DC brushless motor.
In FIG. 8, numeral 501 denotes a motor unit, numeral 502 denotes a control IC, and numeral 503 denotes a three-phase motor. Numeral 504 denotes a Hall sensor which detects a position of a main pole in a rotor. Numeral 505 denotes an FG sensor which detects a pattern adhered magnetically to the rotor, and outputs 36 pulses per one rotation of the motor.
Numeral 506 denotes an oscillator, numeral 507 denotes a current detection resistor, numeral 508 denotes a control unit, numeral 509 denotes a driver unit, numeral 510 denotes a current limiter detection unit, numeral 511 denotes a speed control unit, numeral 512 denotes a frequency divider, and numeral 513 denotes an integrating amplifier. Numerals 514 and 516 denote resistors which are integrating amplifier constants, and numerals 515 and 517 denote capacitors which are also integrating amplifier constants.
Numeral 518 denotes a control signal line which is used to drive and stop the motor from a not-shown microcomputer, and numeral 519 denotes a ready signal line which is activated when the number of rotations of the motor reaches a predetermined value. Further, a motor brake signal line is provided to supply a motor brake signal.
Next, an operation will be explained.
When a motor driving instruction is issued through the control signal line 518 by controlling the image forming apparatus, the control unit 508 detects the position of the main pole in the rotor of the three-phase motor 503 by using the Hall sensor 504, creates a three-phase excitation pattern to rotate the motor in a desired rotation direction, and transmits an excitation signal to a driver unit 509.
In response to the excitation signal, the driver unit 509 excites a not-shown output transistor to change the current direction for the coil of the three-phase motor 503 to obtain desired excitation. On the other hand, when the rotor of the three-phase motor 503 is rotated, a predetermined pulse is generated by the FG sensor 505, and the generated pulse is transferred to the speed control unit 511. The speed control unit 511 compares a reference clock generated by the oscillator 506 and the frequency divider 512 with the pulse detected by the FG sensor 505, and then outputs a difference obtained in the comparison.
The reference clock is set to be the object number of rotations of the motor. Namely, when the FG sensor outputs 30 pulses per one rotation of the motor, the reference clock only needs 600/60xc3x9730=300 Hz to rotate the motor by 600 rpm.
The difference from the object speed obtained by the speed control unit 511 is integrated by the integrating amplifier 513 and transferred to the driver unit 509. At this time, a gain and a phase compensation value are determined by the resistors 514 and 516 and the capacitors 515 and 517.
Such constants are called servo constants.
FIG. 9 is a timing chart showing switchback control timing in sheet feed, sheet transportation and two-faced printing of the conventional image forming apparatus.
In FIG. 9, numeral 601 denotes sheet feed motor driving timing, numeral 602 denotes photosensitive drum driving timing for each color, numeral 603 denotes fixing roller driving timing, numeral 604 denotes sheet discharge sensor output timing, and numeral 605 denotes reverse rotation motor driving timing.
First, when a printing start is triggered at a time 606, the photosensitive drum, the transfer roller, the cartridge driving roller and the electrostatic belt are driven at a time 607. Then, the sheet feed motor is driven at a time 608 to feed and transport the sheet.
After the sheet is transported, when a desired image forming operation ends, the leading edge of the sheet reaches the sheet discharge sensor, and this sensor detects the sheet at a time 609. On the other hand, when the sheet feed and transportation operation becomes unnecessary, the sheet feed motor is stopped at a time 610.
Next, when the trailing edge of the sheet passes the sheet discharge sensor, this sensor detects no sheet at a time 611. Then, a reverse rotation motor is driven at a time 612 to switch back the sheet. When the sheet is transported until a predetermined position at a time 613, the reverse rotation motor is stopped.
Then, when a next printing operation is instructed, an image is formed on the back face of the sheet, whereby the two-faced printing ends.
As described above, in the image forming apparatus which performs the two-faced printing, the reverse rotation motor dedicated to switch back the sheet is provided. Thus, when the trailing edge of the sheet is detected by the sensor, the sheet is switched back and transported by the reverse rotation motor.
Incidentally, in the conventional apparatus, the DC brushless motor capable of achieving high output and high efficiency is used to drive the units such as the photosensitive drum, a development roller acting as the cartridge driving roller, an electrification roller, the fixing roller and the like of which the load torque is relatively large. On the other hand, the pulse motor of low output and low cost is used to drive the units such as the sheet feed unit, the sheet transportation unit, the switchback unit for the twofaced printing, and the like of which the load torque is relatively small.
However, there is a problem that cost performance decreases by adding the pulse motor used only in two-faced printing. Further, there is a problem that a load of the power supply in the image forming apparatus increases because of increase in pulse motor driving power, and thus cost of the power supply unit increases.
As one of the methods to solve these problems, there is an idea that the fixing motor which is disposed at the position closest to the switchback unit is used combinedly for the switchback control. However, the load torque of the fixing motor is large, inertia is large because the DC brushless motor is used, and it takes time to switch back the sheet. Thus, when the forward rotation of the motor is changed to the reverse rotation to switch back the sheet, a distance necessary for the rotation change is long. For this reason, there is a problem that a transportation path length from the sheet discharge sensor to the reverse rotation roller is long, and thus the size of the apparatus is enlarged.
The present invention is made to solve the above problems, and an object thereof is to provide an image forming apparatus which attempts a decrease in cost and a high-speed switchback operation, a control method for the image forming apparatus, and a storage medium.
In order to achieve the above object, the present invention provides an image forming apparatus comprising:
a switchback means for switching back a recording medium of which an image was recorded on one face, to record an image on the other face thereof;
a DC brushless motor for driving the switchback means; and
a control means for performing operation control of the DC brushless motor,
wherein the control means reversely rotates the DC brushless motor for a predetermined time after performing brake control of the DC brushless motor for a predetermined time, at predetermined timing.
Further, the present invention provides a motor driving apparatus comprising:
a control means for controlling driving of a DC brushless motor; and
a setting means for setting a control value of the control means in accordance with a transportation condition of a recording medium,
wherein the control means reversely rotates the DC brushless motor after performing brake control of the DC brushless motor for a predetermined period on the basis of the control value.
Further, the present invention provides a control method for an image forming apparatus which has a switchback mechanism for switching back by using a DC brushless motor a recording medium of which an image was recorded on one face, to record an image on the other face thereof, the method comprising:
a step of performing brake control of the DC brushless motor for a predetermined time at predetermined timing; and
a step of reversely rotating the DC blushless motor for a predetermined time.
Further, the present invention provides a driving method for a DC brushless motor, comprising:
a control step of controlling driving of the DC brushless motor; and
a setting step of setting a control value in the control step in accordance with a transportation condition of a recording medium,
wherein the control step reversely rotates the DC brushless motor after performing brake control of the DC brushless motor for a predetermined period on the basis of the control value.
Other objects, features and effects of the present invention will become apparent from the following detailed description and the attached drawings.